1. Field of the Invention
The present invention relates to a semiconductive roller and a charging roller employing the same, as well as an electrophotographic apparatus including the charging roller.
2. Description of Related Art
An image forming apparatus such as a laser printer, an electrostatic copier, a plain-paper facsimile or a composite apparatus thereof includes a charging roller and a developing roller.
The charging roller uniformly charges the surface of a photosensitive body in the image forming apparatus. The developing roller develops an electrostatic latent image formed by exposing the charged surface of the photosensitive body into a toner image by sticking a toner thereto.
In general, a semiconductive roller including a roller body made of a semiconductive rubber composition, a coating film made of urethane-based resin or the like covering the outer peripheral surface of the roller body and a shaft made of metal or the like inserted into the center of the roller body, for example, has been employed as this type of charging roller or developing roller (refer to Japanese Patent No. 3449726, for example).
The coating film is provided for preventing the components of the semiconductive rubber composition from bleeding on the outer peripheral surface of the roller body and thereby staining the photosensitive body directly coming into contact with the charging roller or the developing roller. In other words, the coating film is provided for preventing influence exerted on the formed image due to staining of the photosensitive body. Further, the coating film is provided also for preventing an additive such as silica added to the toner for improving flowability and chargeability thereof from being accumulated on the outer peripheral surface of the roller body to influence the formed image.
The coating film is formed by applying the raw material (a liquid coating agent) therefor to the outer peripheral surface of the roller body by a method such as spraying or dipping and drying the applied raw material.
However, this method easily results in various defectives such as contamination with foreign matter such as dust, irregularity in thickness etc. in the process of forming the coating film. Further, this method is an already established technique, and allows only small room for further improvement. Therefore, it is difficult to remarkably reduce the rate of defectives (the rejection rate). This results in reduction of the yield and productivity of the semiconductive roller and increase in the manufacturing cost.
As a method of forming a coating film different from the aforementioned one, a method of forming a roller body by a semiconductive rubber composition containing diene rubber and oxidizing the diene rubber by irradiating the outer peripheral surface of the roller body with ultraviolet light thereby forming a coating film (an oxide film) is proposed (refer to Japanese Unexamined Patent Publication No. 2004-176056, for example).